Cardiac computed tomography using redundant-ray prospective gating

A fourth-generation, computed tomographic (CT) scanner, equipped for prospectively gated cardiac imaging, was modified to control the scan data acquisition by using knowledge of the location of redundant rays in the sinogram. In conventional prospective gating, a computer monitors the electrocardiogram (ECG) and calculates when to initiate the next scan in a gated series in order to acquire all 360 degrees of projection data for a desired phase of the cardiac cycle. However, in each scan of a series, every projection ray is measured twice (when the positions of the source and detector are reversed). Redundant-ray prospective gating takes advantage of this information to improve the efficiency of data acquisition. Using a heart phantom "beating" at 90 min-1, images of all phases of the cardiac cycle with 100-ms temporal resolution were obtained in four scans with redundant-ray gating; whereas a four-scan series with conventional prospective gating yielded worse images of 170-ms resolution.